1. Field of the Invention
The present invention relates to a texture mapping method.
The computer graphics field has been attempting to visibly represent, in a manner in which a user can easily understand relevant contents, geometric data produced through a computer-aided design (CAD). In such an attempt, a texture mapping technology may be used. The texture mapping technology will now be described. Through the texture mapping technology, it can be relatively easily realized that geometric data is visibly represented so that a represented image resembles a relevant real object. In the texture mapping technology, previously provided images are used to cover a represented object surface to be displayed. As an example of such a process, images are produced from photographs of a surface of the earth, and/or a road surface, and the thus produced images are used to cover a represented surface of the earth and/or road surface serving as a background of an image of a building, the building image being produced through CAD or the like. Such images used to cover such a desired object surface will be referred to as texture or texture images.
2. Related Art
In such a texture mapping method, as shown in FIG. 1A, a texture image 10 is mapped onto an area 11a of a surface of an object 11 so that the texture image 10 is placed on the area 11a of the surface of the object 11. Coordinates (u, v) of the texture image 10 in its image space correspond to coordinates (p, q) of the area 11a in the mapping. An operation of such a mapping process will now be described with reference to FIG. 1B. A step S2 (the term `step` will be omitted, hereinafter) calculates the coordinates (p, q) in the area 11a. S4 calculates the corresponding coordinates (u, v) in the texture image 10 in its image space. S6 reads color data of the texture image 10 according to the thus calculated coordinates (u, v) and determines color data of a position specified by the coordinates (p, q) in the area 11a to be the thus read color data. Such a process is repeated for all coordinates in the area 11a so that the color data for all the area 11a on the object 11 is determined to be the corresponding color data of the texture image 10.
In the texture mapping method, a plurality of identical texture images 10 are placed on a desired object surface so that the object surface is covered thereby. Thus, as shown in FIG. 2, identical texture images 10, each image representing a pattern of a surface such as an earth surface, a road surface, a lawn surface or the like, are orderly and closely placed on a wide object surface 12 as shown in the figure for example. As a result, as shown in the figure, there appears periodicity in the object surface 12, such periodicity giving a strange impression adversely affecting real appearance of the object surface 12 and thus being an undesirable one. Causes of such periodicity include discontinuities occurring at each boundary between adjacent texture images 10 and repetition of the same patterns caused by repeatedly side-by-side arranged identical texture images 10.